1. Field of the Invention
The present invention relates to an apparatus for forming a diamond-like thin film by using ionized particles of hydrocarbon gas.
2. Description of the Prior Art
A diamond-like thin film has physical properties similar to those of diamond, and it is applied to various electronics devices. Various kinds of apparatuses of depositing a diamond-like thin film are disclosed already. Among them, an apparatus disclosed in Japanese Patent laid open Publication No. 65,796/1985 shown in FIG. 1 has a relatively simple structure.
In the prior art apparatus, after ethylene gas 27 is supplied to a vacuum chamber 26, a filament 28 is heated with an electric power source 29 for generating thermoelectrons. At the same time, a positive electric potential is applied to an acceleration electrode 30 to accelerate the thermoelectrons. Then, the thermoelectrons collide with the ethylene gas to generate a plasma (not shown) of the ethylene gas. The plasma includes many ionized particles of the hydrocarbon gas. By applying a negative electric potential to a substrate 32 for accelerating ionized particles, these ionized particles deposit on the substrate 32 to form a diamond-like thin film.
However, the above-mentioned prior art apparatus has problems on the film thickness, the film quality, the deposition rate, the spark-like anomalous discharge and the contamination of the vacuum chamber. That is, the film thickness and the film quality are difficult to be realized to be uniform. Still further, anomalous spark-like discharge is liable to arise in the vacuum chamber 26 though it depends on synthesis conditions, so that it becomes difficult to prepare a diamond-like film stably in some cases. Further, almost all of the vacuum chamber 26 is liable to be contaminated with a deposit, and the maintenance operation such as cleaning of the vacuum chamber 26 is troublesome.
In another example of a prior art apparatus for forming a diamond-like thin film by using ionized particles of hydrocarbon gas, a Kaufman type ion source is used to generate and accelerate ionized particles of hydrocarbon to deposit a diamond-like thin film on a substrate (refer the Proceeding of the 36-th Meeting of the Japanese Society of Applied Physics 1p-H-14). The prior art apparatus has an ionized particle generator such as the Kaufman type ion source including an ionization chamber provided in a vacuum chamber wherein a substrate is provided, and a plasma of hydrocarbon is generated in the ionization chamber. The ionized particles are accelerated by applying a negative high voltage to the substrate.
If the Kaufman type ion source is used, the plasma is contained in the ionization chamber and the ionized particles come to the substrate straightly as a beam, so that the plasma becomes harder to extend outside the ionization chamber in the vacuum chamber if compared with the abovementioned apparatus of the Japanese Patent laid open Publication No. 65,796/1985. Then, the film thickness, the film quality, the deposition rate, the spark-like anomalous discharge and the contamination of the vacuum chamber are improved.
However, in the Kaufman type ion source and the like, though the ionized particles fly to the substrate straightly as a beam, there are also ions which fly to components other than the substrate in the vacuum chamber. Especially when a diamond-like thin film is deposited on a wide area of substrate which has a size equal to or larger than the opening of the ionized particle generator, the film thickness becomes thinner towards the periphery of the substrate.
As explained above, the prior art apparatuses have problems to be solved such as the uniform film thickness and film quality, the deposition rate, the stable preparation and the maintenance of a diamond-like thin film.